WHEN APPLE INTRODUCED its iBook laptop for consumers and students two years ago, it received a lukewarm reception. That’s because it managed to combine a heavy, wide design with a miserly amount of memory and hard-disk capacity. It seemed designed more for junior high schools than for consumers or college students.This month, Apple fixed all that with a totally revised iBook that shares nothing with its predecessor. Instead, it looks like the little brother of the company’s spectacular top-of-the-line Titanium PowerBook. It has a much better blend of features that will appeal to home consumers and students.